Mayumi Shimada

The use of polylactic acid/polyglycolic acid copolymer and gelatin sponge complex containing human recombinant bone morphogenetic protein-2 following condylectomy in rabbits.

PURPOSE To examine the results of a polylactic acid/polyglycolic acid copolymer and gelatin sponge complex (PGS) with or without recombinant human bone morphogenetic protein-2 (rhBMP-2) used to treat condylar defects in rabbits. MATERIAL AND METHODS Adult male Japanese white rabbits (n=60; 3kg; 12-16 weeks old) were divided into three groups of 20 each. All rabbits underwent condylectomy. In the two implanted groups, PGS with or without 5 microg of rhBMP-2 was implanted to the condylar defect without fixation. No material was implanted into the control group. Animals were sacrificed at 2, 4, 8, 12 and 24 weeks postoperatively, and the temporomandibular joints (TMJs) were examined histologically. RESULTS Four weeks after implantation, growth of bone and cartilage-like tissue was observed in all rabbits that received PGS implants (with and without rhBMP-2). A cartilage-like layer was derived from the bone marrow at the operated surface. There was no growth of bone tissue in the control rabbits, but they also had a cartilage-like layer directly derived from the operated surface. CONCLUSION This study demonstrated that PGS with or without rhBMP-2 could induce regeneration of new bone and cartilage-like tissue in the TMJ.

Hepatocyte growth factor is essential for migration of myogenic cells and promotes their proliferation during the early periods of tongue morphogenesis in mouse embryos

Temporal and spatial occurrence of hepatocyte growth factor (HGF) and its cognate receptor c‐Met in the mouse mandibular development was investigated by immunohistochemistry and quantitative reverse transcriptase‐polymerase chain reaction. HGF was first recognized in the mesenchymal cells of the first branchial arch at the 10th day of gestation (E10), before tongue formation, whereas HGF receptor (c‐Met) ‐positive myogenic cells first appeared at E11 in the center of mandibles. By E12, HGF turned to be colocalized with c‐Met in the differentiating tongue myoblasts. Between E14 and E16, HGF disappeared, whereas c‐Met remained, in the tongue myoblasts. The levels of HGF mRNA in the developing tongue decreased in accordance with the increase of desmin mRNA levels from E11 to E17. These in vivo results strongly suggest that the HGF/c‐Met system takes part in the earlier stages of tongue development. To elucidate this hypothesis, the antisense oligodeoxyribonucleotide (A‐ODN) for mouse HGF mRNA was added to the organ culture system of mandible with serumless, defined medium. Mandibular arches from E10 mouse embryos were cultured at 37°C for 10 days in the absence or presence of A‐ODN, control (sense) oligonucleotide (C‐ODN), or A‐ODN plus recombinant HGF. In the control mandibular explants cultured without HGF or ODN, the anterior two‐third of the tongue derived from the first branchial arch was formed. It contained abundant desmin‐positive myoblasts and was equivalent to the tongue of E14–E15. In contrast, in the presence of A‐ODN in the medium, neither the swelling nor myogenic cells were found in the tongue‐forming region of explants, and myogenic cells accumulated behind the tongue‐forming region. Such dysplasia of tongue was never induced in the presence of C‐ODN or A‐ODN plus recombinant HGF in the medium. The effect of A‐ODN appeared to be developmental stage‐specific, because tongue dysplasia occurred when A‐ODN was present during the earlier 4 days but not during the later 4 days of the culture. Furthermore, recombinant HGF added to the culture without ODNs during the earlier 4 days caused elevation in the number of mitotic myoblasts. These results suggest that HGF regulates both the migration and proliferation of myogenic cells during the earlier stages of tongue development.

Different expression of 25-kDa heat-shock protein (Hsp25) in Meckel's cartilage compared with other cartilages in the mouse

The 25-kDa heat-shock protein (Hsp25) is expressed in the cartilage of the growth plate and suggested to function in chondrocyte differentiation and degeneration. Using immunohistochemistry, we examined the temporal and spatial occurrence of Hsp25 in Meckels cartilage in embryonic mice mandibles, and in other types of cartilage in both embryonic and adult mice. In adults, Hsp25 immunoreactivity was detected in the hypertrophic chondrocytes located in growth plates of long bones and in non-osteogenic laryngeal and tracheal cartilages. No chondrocytes in the resting or proliferating phase exhibited Hsp25 immunoreactivity. In the embryonic mandibles, resting and proliferating chondrocytes in the anterior and intermediate portions of Meckels cartilage showed Hsp25 immunoreactivity from the 12th day of gestation (E12) through E15, whereas those in the posterior portion showed little or no immunoreactivity. After E16, the overall Hsp25 immunoreactivity in Meckels cartilage substantially reduced in intensity, and little or no immunoreactivity was detected in the hypertrophic chondrocytes located in the degenerating portions of Meckels cartilage. The antisense oligonucleotide for Hsp25 mRNA applied to the culture media of the mandibular explants from E10 embryos caused significant inhibition of the development of the anterior and middle portions of Meckels cartilage. These results suggested that Hsp25 is essential for the development of Meckels cartilage and plays different roles in Meckels cartilage from those in the permanent cartilages and the cartilages undergoing endochondral ossification.

Transient occurrence of 27 kDa heat‐shock protein in the terminal tubule cells during postnatal development of the rat submandibular gland

It has been suggested that the 27 kDa heat‐shock protein (Hsp27) plays a role at crucial cellular checkpoints for proliferation, apoptosis, and differentiation. We examined the immunolocalization of Hsp27 in the rat submandibular gland during postnatal development, wherein acinar cells proliferate and differentiate at earlier postnatal periods. At 2 weeks of age, weak Hsp27 immunoreactivity was distributed diffusely over all gland components. At 3 weeks, Hsp27 immunoreactivity disappeared in most parts of the acini and ducts, but was intensely accumulated in a small cell population located in the acinar center. This population was composed mostly of terminal tubule (TT) type I cells. At 4 weeks, the Hsp27‐immunopositive cell population in the acinar center was composed primarily of immature (type II) acinar cells, partly of immature (granulated) intercalated duct (ID) cells, and occasionally of apoptotic cells. After 5 weeks, all acinar components became mature and were no longer immunoreactive for Hsp27. When acinar cell differentiation was accelerated by administration of isoproterenol to 3‐week‐old rats for 7 days, the number of Hsp27‐positive cells was significantly lower than in the control gland at 4 weeks, confirming that Hsp27 expression is downregulated in mature acinar cells. These results suggest that at around 3–4 weeks in postnatal development, the centroacinar TT cells stop proliferating and begin to differentiate into acinar and ID cells, and occasionally undergo apoptosis. Hsp27 is transiently expressed in the centroacinar TT cells during this critical period, and thus may play a role in their differentiation into the immediate descendants. Anat Rec 264:358–366, 2001.